Method of determining glucose concentration of a whole blood sample

ABSTRACT

A total transmission spectroscopy system for use in determining the analyte concentration in a fluid sample comprises a sample cell receiving area, a light source, a collimating lens, a first lens, a second lens, and a detector. The sample cell receiving area is adapted to receive a sample to be analyzed. The sample cell receiving area is constructed of a substantially optically clear material. The collimating lens is adapted to receive light from the light source and adapted to illuminate the sample cell receiving area with a substantially collimated beam of light. The first lens is adapted to receive regular and scattered light transmitted through the sample at a first angle of divergence. The first lens receives light having a first angle of acceptance. The first lens outputs light having a second angle of divergence. The second angle of divergence is less than the first angle of divergence. The second lens is adapted to receive light from the first lens and adapted to output a substantially collimated beam of light. The detector is adapted to measure the light output by the second lens.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/834,639,filed on Jul. 12, 2010, which has been allowed; application Ser. No.12/834,639 is a divisional of application Ser. No. 11/791,556 filed onMay 23, 2007, which has issued as U.S. Pat. No. 7,787,109; applicationSer. No. 11/791,556 is the national phase of Application No.PCT/US2005/045233 filed on Dec. 12, 2005, that claims priority back toProvisional Application No. 60/635,666 filed on Dec. 13, 2004.

FIELD OF THE INVENTION

The invention generally relates to spectroscopy and, more particularly,to the use of total transmission spectroscopy for determining theconcentration of an analyte in body fluid.

BACKGROUND OF THE INVENTION

Transmission spectroscopy is used to perform quantitative analysis of asample based on the transmission of a light beam through a samplecontained by a sample cell. Different frequency components of the lightbeam are absorbed by components of the sample, whereby a frequencyanalysis of light transmitted through the sample permits analysis of thesample itself. Dry chemical reagents are dissolved by the sample andreact with the analyte of interest to produce a chromaphoric response atcertain wavelengths of light ranging from about 450 nanometers (“nm”) toabout 950 nm.

Transmission spectroscopy is one method for measuring the concentrationof an analyte (e.g., glucose, lactate, fructosamine, hemoglobin A_(1c),and cholesterol) in a body fluid (e.g., blood, plasma or serum, saliva,urine, and interstitial fluid). An indicator reagent system and ananalyte in a sample of body fluid are reacted to produce a chromaticreaction—the reaction between the reagent and analyte causes the sampleto change color. The degree of color change is indicative of the analyteconcentration in the body fluid. The color change of the sample isevaluated, for example, using spectroscopy to measure the absorbancelevel of the transmitted light. Regular transmission spectroscopy isdescribed in detail in U.S. Pat. No. 5,866,349. Diffuse reflectance andfluorescence spectroscopy is described in detail in U.S. Pat. No.5,518,689 (entitled “Diffuse Light Reflectance Readhead”); U.S. Pat. No.5,611,999 (entitled “Diffuse Light Reflectance Readhead”); and U.S. Pat.No. 5,194,393 (entitled “Optical Biosensor and Method of Use”).

At a rudimentary level, a transmission spectroscopic analysis includes alight source that produces a beam of light for illuminating a sample anda detector for detecting light that is transmitted through the sample.The detected transmitted light is then compared to a reference sample(e.g., light from the source directly detected by the detector withoutthe sample present). Regular transmission spectroscopy refers to thecollection and analysis of the light that exits the sample at smallangles (e.g., from about 0° to about) 15° relative to the normal opticalaxis, and not the scattered light transmitted through the sample. Thenormal optical axis is an axis that is perpendicular to the sample celloptical entrance and exit widows. Total transmission spectroscopy refersto the collection of substantially all of the light (including scatteredlight) exiting a sample at large angles (e.g., from about 0° to about)90° relative to the normal optical axis. Existing systems for totaltransmission spectroscopic analysis implement an integrating sphere forcollecting all of the light passing through the sample, and a requiredphotomultiplier tube for reading the reflected light from a smallportion of the inside surface of the integrating sphere.

As reported in an article entitled “Data Preprocessing and Partial LeastSquares Analysis for Reagentless Determination of HemoglobinConcentration Using Conventional and Total Transmission Spectroscopy,”which appeared in the April 2001 of the Journal of Biomedical Optics(Vol. 6, No. 2), regular transmission levels (scatter excluded) of wholeblood has hemoglobin concentrations ranging from about 6.6 to 17.2 g/dLare 15.8 to 0.1% T throughout the visible and near-infrared range (e.g.,about 500 nm to about 800 nm) with a pathlength of only 100 μm; but,total transmission levels (scatter included) of whole blood hashemoglobin concentrations within the same range are 79% T to 2% T. Thetotal transmission of light having a wavelength ranging from about 600nm to about 800 nm is nearly 100% T, and there is little separationbetween the different hemoglobin levels. Thus, the hemoglobinconcentration level has little impact on the transmitted light having awavelength ranging from about 600 nm to about 800 nm.

A drawback associated with existing total transmission spectroscopysystems that use an integrating sphere is a low signal level thatrequires using a photomultiplier tube for reading the reflected lightfrom a small portion of the inside surface of the integrating sphere.Another drawback associated with conventional total transmissionspectroscopy systems is the cost of an integrating sphere andphotomultiplier tube. The cost of these devices makes itcost-prohibitive to produce existing total transmission spectroscopysystems for use by a patient needing to self-test, for example, thepatient's blood-glucose concentration level. As a result, spectroscopicsystems for use in determining the analyte concentration in body fluidshave centered on regular transmission measurements.

Existing systems using regular transmission spectroscopy also haveseveral drawbacks. As discussed above, only the light emerging from thesample at small angles is collected using existing regular transmissionspectroscopy measurements, often resulting in losing light exiting thesample at large angles. A significant portion of light scattered by thered blood cells is not collected with existing systems using regulartransmission measurements, which can lead to significant loss of lightresulting in very low transmission levels through whole blood.

To reduce the transmission losses using existing regular transmissionsystems, a reagent or detergent is typically added to the blood sampleto lyse the red blood cells. Rupture of the cell walls through lysis ofthe blood cells reduces the scattered transmission, and increases theregular transmission of light through the sample. The addition of alysing reagent and subsequent lysis of the red blood cells is timeconsuming relative to the overall measurement process. This problem isnot present in existing total transmission spectroscopy methods becausethe scattered transmitted light and regular transmitted light iscollected by the optics. Total transmission levels are typically highenough that lysing the red blood cells is not required, whichsignificantly reduces the overall time for a chemical assay.

Another drawback associated with existing systems using regulartransmission spectroscopy is a transmission bias at wavelengths of lightwhere the chromatic reaction occurs. The indicator reagent may reactwith intracellular components (i.e., hemoglobin, lactate dehydogenase,etc.) released from the lysing of red blood cells causing an additionalcolor response. The transmission bias caused by this reaction of thereagent and the certain intracellular components such as hemoglobin isnot indicative of the blood-glucose level. This transmission bias causesinaccuracies in determining the analyte (e.g., glucose) concentration.The amount of bias is related to the concentration of certain cellularcomponents in the blood cells.

Since blood lysis is not required for existing total transmissionspectroscopy methods, the amount of intracellular components that mayinterfere with the glucose measurement is significantly reduced. Bias,however, remains for substances such as hemoglobin that absorb atvisible wavelengths less than about 600 nm. It is known from theaforementioned article in the Journal of Biomedical Optics, for example,that total transmission spectra of oxy-hemoglobin has absorbance peaksat wavelengths of about 542 nm and about 577 nm. It is known that theabsorbance level at wavelengths of about 542 nm or about 577 nm may beused to determine the hemoglobin concentration of the whole bloodsample. The remaining interference error in glucose concentration causedby hemoglobin may be corrected for by measuring the total transmissionat 542 nm or 577 nm, and correlating the absorption to known hemoglobinconcentration.

The hematocrit level of whole blood may also cause a total transmissionbias due to differences in the amount of scattered light at differenthematocrit levels. The transmission loss caused by varying levels ofhematocrit is not indicative of the blood-glucose level. Existingsystems using regular transmission or total transmission spectroscopyare not capable of detecting the difference in hematocrit levels becauseof poor transmission level and poor separation between hematocrit levelsat certain wavelengths of light.

Another drawback to existing systems using regular transmissionspectroscopy is accuracy errors that result from the sample path length.A 10% variation in the path length of the sample cell area results in a10% error in the concentration measurement for both regular and totaltransmission methods. The mechanical tolerance that causes the pathlength variation is substantially the same regardless of the pathlength. Existing systems using regular transmission methods, however,require a shorter path length to make up for transmission losses due tored blood cell scatter. Thus, the mechanical tolerance at a shorterpathlength results in higher concentration errors. A longerpathlength—permitted by total transmission spectroscopy systems thatcollect scattered light from red blood cells—reduces pathlength error.

Therefore, it would be desirable to reduce or eliminate the abovedescribed problems encountered by existing systems using regular ortotal transmission spectroscopy in determining analyte concentration inbody fluid.

SUMMARY OF THE INVENTION

According to one embodiment, a total transmission spectroscopy systemfor use in determining the concentration of an analyte in a fluid samplecomprises a sample cell receiving area, a light source, a collimatinglens, a first lens, a second lens, and a detector. The sample cellreceiving area is adapted to receive a sample to be analyzed. The samplecell receiving area is constructed of a substantially optically clearmaterial. The collimating lens is adapted to receive light from thelight source and adapted to illuminate the sample cell receiving areawith a substantially collimated beam of light. The first lens is adaptedto receive regular and scattered light transmitted through the sample ata first angle of divergence. The first lens receives light having afirst angle of acceptance. The first lens outputs light having a secondangle of divergence. The second angle of divergence is less than thefirst angle of divergence. The second lens is adapted to receive lightfrom the first lens and adapted to output a substantially collimatedbeam of light. The detector is adapted to measure the light output bythe second lens.

According to one method, the analyte concentration in a fluid sample isdetermined with a total transmission spectroscopy system. A sample to beanalyzed is received in a sample cell receiving area of the totaltransmission spectroscopy system. A beam of light is outputted via alight source. The beam of light output is substantially collimated fromthe light source. The sample is illuminated with the substantiallycollimated beam of light output from the light source. Regular andscattered light transmitted through the sample is collected with a firstlens. The angle of divergence of the transmitted light is reduced withthe first lens. The light having a reduced angle of divergence isreceived with a second lens. The received light is substantiallycollimated with the second lens. The substantially collimated light fromthe second lens is measured with a detector.

According to one method, light transmitted through a fluid sample ismeasured with a total transmission spectroscopy system. The sample isilluminated with a substantially collimated beam of light. Regular andscattered light transmitted through the sample is collected with a firstlens. The angle of divergence of the transmitted light is reduced withthe first lens. The transmitted light is substantially collimated with asecond lens after reducing the angle of divergence. The substantiallycollimated transmitted light is measured with a detector.

According to another method, the concentration of an analyte in a fluidsample is measured using a total transmission spectroscopy system. Thesystem includes a collimated light source, a sample receiving area, afirst lens being adapted to receive regular and scattered lighttransmitted through the sample, a second lens being adapted to receivelight from the first lens and adapted to output a substantiallycollimated beam of light, and a detector. The sample reacts with areagent adapted to produce a chromatic reaction in a sample cellreceiving area of the system. The sample is illuminated with asubstantially collimated beam of near-infrared light output by the lightsource of the system. The near-infrared light transmitted through thesample is measured with a detector of the system. The sample isilluminated with a substantially collimated beam of visible light outputby the light source of the system. The visible light transmitted throughthe sample is measured with the detector. A ratio of the measuredvisible light to the measured near-infrared light transmitted throughthe sample is determined.

According to yet another method, the glucose concentration in a bloodsample is determined using a total transmission spectroscopy system. Thesystem includes a first lens adapted to receive regular and scatteredlight transmitted through the sample and a second lens adapted toreceive light from the first lens and adapted to output a substantiallycollimated beam of light. The method comprises reacting the blood samplewith a dried reagent to produce a chromatic reaction in a sample cellreceiving area. The sample is illuminated with a substantiallycollimated beam of visible light output by a light source of the system.The visible light is transmitted through the sample is measured with adetector of the system. The sample is illuminated with a substantiallycollimated beam of near-infrared light output by the light source. Thenear-infrared light transmitted through the sample is measured with thedetector. A correction is made for the transmission bias caused by thehematocrit level of the blood sample. The glucose concentration in theblood sample is determined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a side view of a total transmission spectroscopy system foruse in determining the analyte concentration in body fluid according toone embodiment of the present invention.

FIG. 1 b is a side view of a total transmission spectroscopy system foruse in determining the analyte concentration in body fluid according toanother embodiment of the present invention.

FIG. 2 a is a flow chart illustrating the operation of the system ofFIG. 1 a according to one embodiment of the present invention thatincludes an underfill detection for determining if there is an adequatesample size.

FIG. 2 b is a flow chart illustrating the operation of the system ofFIG. 1 a according to a further embodiment of the present invention thatis capable of correcting for transmission bias caused by hematocritlevels in the blood sample.

FIG. 2 c is a flow chart illustrating the operation of the system ofFIG. 1 a according to another embodiment of the present invention thatis capable of correcting for transmission bias caused by hemoglobin in ablood sample.

FIG. 3 a is a plot of the total transmission spectra of reacted glucoseassays with 20% hematocrit whole blood at 54, 105, 210, and 422 mg/dLglucose levels through the visible and near-infrared spectrum from 500nm to 940 nm.

FIG. 3 b is the total transmission spectra of reacted glucose assayswith 60% hematocrit whole blood at 59, 117, 239, and 475 mg/dL glucoselevels through the visible to near-infrared spectrum from 500 nm to 940nm.

FIG. 4 a is a plot of the total transmission spectra of FIG. 3 acorrected for scatter by ratioing all transmission readings to thetransmission at 940 nm.

FIG. 4 b is the total transmission spectra of FIG. 3 b corrected forscatter by ratioing all transmission readings to the transmission at 940nm.

FIG. 5 is a plot of the glucose concentration dose response of wholeblood at 20%, 40%, and 60% levels of hematocrit measured with totaltransmission (in absorbance units) at 680 nm, obtained using thereadhead of FIG. 1 a.

FIG. 6 is a plot of the dose response of FIG. 5 corrected fortransmission bias (in absorbance units) caused by different hematocritlevels in a blood sample.

FIG. 7 is a plot of the total transmission (spectrum in absorbanceunits) of reagent with whole blood at 0, 100, and 400 mg/dL glucoselevels, and water with reagent throughout the visible and near-infraredspectrum from 500 nm and 940 nm.

FIG. 8 plots the linear response of total transmission (in absorbanceunits) at 680 nm of reagent reacted with whole blood at glucoseconcentrations of 0, 50, 100, 200, and 450 mg/dL.

FIG. 9 shows the regular and total transmission spectrums from 500 nm to940 nm for whole blood at 20%, 40%, and 60% levels of hematocrit.

While the invention is susceptible to various modifications andalternative forms, specific embodiments are shown by way of example inthe drawings and are described in detail herein. It should beunderstood, however, that the invention is not intended to be limited tothe particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Turning now to the drawings and first to FIG. 1 a, there is shown atransmission spectroscopy system 10 implementing total transmissionspectroscopy for use in the determination of an analyte concentration ina biological sample such as a body fluid. Non-limiting examples ofanalytes that may be determined include glucose, lactate, fructosamine,cholesterol, hemoglobin A_(1c), and cholesterol. Such analytes may be inbody fluids such as blood (including blood plasma and serum), saliva,urine, and interstitial fluid.

The system 10 includes a light source 12. According to one embodiment,the light source is a halogen lamp that outputs a beam of white lighthaving a wavelength ranging from about 300 nm to about 3200 nm.According to another embodiment, the light source 12 outputs two or morebeams of monochromatic light using light emitting diodes (LEDs) havingcenter wavelengths located within a wavelength range from about 400 nmto about 1000 nm. The light output by the light source 12 is received bya collimation lens 22 that outputs a substantially collimated beam oflight 14. The collimated beam of light 14 illuminates a sample 16disposed in a sample cell receiving area 18 of a readhead 20.

According to one embodiment, the sample comprises blood with glucosethat has reacted with a dry reagent system containing an indicator.According to one embodiment, a glucose-indicator reagent that may beused contains glucose dehydrogenase, NAD (nicotinamide adeninedinucleotide), diaphorase, tetrazolium indicator (WST-4)(2-benzothiazoyl-3-(4-carboxy-2-methoxyphenyl)-5-[4-(2-sulfoethylcarbamoyl)phenyl]-2H-tetrazolium),and polymers. It is contemplated that one skilled in the art may usedifferent enzymes (such as PQQ-glucose dehydrogenase, glucose oxidase,or lactate dehydrogenase, etc.), indicators and mediators, and analytes(such as glucose, lactate, etc.). The reagent formulation does notrequire a hemolyzing agent to break apart red blood cells. By notbreaking apart red blood cells, the total time test is faster.

The substantially collimated beam of light 14 illuminates the sample 16and a portion of light is transmitted through the sample 16. The lightthat is transmitted through the sample, which comprises regular anddiffusely scattered light, is collected by a first lens 30 and a secondlens 40. In the illustrated embodiments, the first and second lenses arehalf-ball lenses. It is contemplated that other types of lens includingball lenses or aspheric lenses may be used to collect the transmittedlight.

According to alternative embodiments, the first lens 30 collects lightat an acceptance angle of about 72°, or a numerical aperture (NA) ofabout 0.951, but the acceptance angle ranges from 0° to 90° forcollecting the scattered portion of the transmitted light. The light 32exiting from the first lens 30 diverges at an angle ranging from about15° to about 40°, and more specifically at an angle about 20°. Thesecond lens 40 reduces the diverging light output 32 of the first lens30 to an angle of diverging light 42 ranging from 0 to about 10 degrees,and is more specifically collimated from 0 to about 5 degrees. Theregular and scattered transmitted light emerging from the sample is notdiverted or scattered by the first and second lenses 30, 40. Thus, thepair of lenses 30, 40 collects substantially all of the lighttransmitted through the sample 16. The pair of lenses 30, 40substantially collimates the collected light and illuminates a detector50 with nearly normal incidence. The diverging light 42 has an angle ofdivergence of less than about 5°.

According to one embodiment of the spectroscopy system 10, a bandpassfilter 52 or a plurality of bandpass filters may be placed before thedetector 50. The bandpass filter(s) 52 typically has a centerwavelength(s) of from about 400 to about 1000 nm, and a narrow bandwidthfrom about 5 to about 50 nm. The bandpass filter(s) 52 are typicallyused when a white light such as a halogen lamp is used as the lightsource 12. Alternatively, a bandpass filter may be used to modify thespectral bandwidth of an LED source 12, or filter out stray ambientlight that does not contribute to the sample transmission. The diverginglight 42 onto the bandpass filter(s) 52 is substantially collimatedbecause light passing through the filter that is outside the filter'sprescribed angle of incidence will not be within the specified bandwidthof the filter.

The first and second lenses 30, 40 combine to improve the signal levelof the light guided to the detector 50 because the lenses 30, 40 collectand guide a high percentage of the light transmitted through the sample16 to the detector 50. Further, signal level is improved by illuminatingthe detector 50 with a collimated beam of light that is substantiallynormal to the surface of the detector. Typically, the angle ofdivergence of the collimated beam of light is less than about 5 degrees.A normal incidence angle to the surface of the detector 50 reducessignal loss caused by Fresnel reflection off the surface of the detector50. A significant light loss is caused by Fresnel reflection at anglesof incidence greater than about 20 degrees.

The light 42 collected by the detector 50 is then compared to areference measurement comprising a reading taken with no sample (air) inthe optical path for determining the percent transmission of the sampleand subsequent analyte concentration in the sample.

According to the illustrated embodiment of the spectroscopy system 10,the detector 50 and bandpass filter(s) 52 are substantially linearlyaligned with the second lens 40. According to one embodiment of thepresent invention, the detector 50 is a silicon detector. However, otherlight detectors including other types of photodetectors such as leadsulfide, for example, or charged coupled devices (CCD) may be used fordetecting the transmitted light. In other alternative embodiments, thedetector 50 and bandpass filter(s) 52 are not linearly aligned with thesecond lens 40, but rather a light guide or a optical fiber(s) (notshown) having an inlet substantially linearly aligned with the secondlens 40 pipes the light to a detector/filter positioned elsewhere, or toa spectrograph. The spectroscopy system 10 significantly improves thesignal level obtained over existing total transmission spectroscopysystems because the light is directly coupled to the detector with thefirst and second lenses 30, 40.

According to one embodiment of the present invention, the path lengththrough the sample 16 is from about 40 μm to about 200 μm and the samplehas a diameter of about 1 mm. According to one embodiment, the firstlens 30 is a plastic micro half-ball lens having a diameter of about 4mm. The second collection lens 40 is a plastic micro half-ball lenshaving a diameter of about 8 mm. The ratio of the diameters of the firstlens and the second lens is generally from about 1:2. The first andsecond half-ball lenses 30, 40 are constructed of acrylic according toone embodiment.

The detector 50 outputs a signal indicative of the amount of receivedlight. According to one embodiment of the present invention, that outputis monitored by a control system (not shown) of the transmissionspectroscopy system 10 comprising the readhead 20 for determining when asample has entered and filled the sample cell receiving area 18 of thereadhead 20. In some embodiments of the present invention, the samplecell receiving area 18 may be part of a capillary channel, or is coupledto a capillary channel for filling the sample cell receiving area 18.The sample cell receiving area 18 is made of a substantially opticallyclear material according to one embodiment.

Turning now to FIG. 1 b, there is shown a transmission system 60 that isused for determining an analyte concentration in a fluid sampleaccording to another embodiment. The transmission system 60 has many ofthe same components that have been described above in connection withFIG. 1 a. Additionally, the transmission system 60 includes a couplinglens 62 that collects the diverging light 42. The coupling lens 62further reduces the diverging light 42 to a diverging light 64 beforereaching an optical cable 66. As shown in FIG. 1 b, the optical cable 66pipes the diverging light to a spectrograph 68. In another embodiment,the spectrograph may be replaced by a detector (e.g., detector 50) shownin FIG. 1 a. In such an embodiment, a filter may be added such as (e.g.,filter(s) 52) described above in connection with FIG. 1 a.

To prevent or inhibit errors associated with (a) underfilling the samplecell receiving area 18, or (b) timing, a control system monitors theoutput of the detector, which changes as the sample cell receiving area18 fills with a body fluid (e.g., blood). A timing sequence, anembodiment of which is described in connection with FIG. 2 a, allowssufficient time for the reaction between the reagent and the analyte inthe sample to occur. This improves the overall performance of thetesting because substantially precise timing may result in a faster andmore reliable analyte determination.

Underfilling occurs, for example, when too little sample is collected toreact with the predetermined amount of reagent placed in the sample cellreceiving area 18. Once transmitted light is detected indicative of afilled sample cell receiving area 18, the control system knows thesubsequent output of the detector 50 may be used for determining theanalyte concentration in the body fluid sample (e.g., blood sample).

Additionally, according to one process of the present invention, oncethe detector 50 detects a sample, or a specific sample amount, thesystem 10 initiates a timing sequence at the conclusion of which thedetector 50 begins to detect light transmitted through the sample foranalysis. According to this process, the transmission spectroscopysystem 10 described in connection with FIG. 2 a begins with monitoringthe sample area to determine the correct time for initiating thetransmitted-light collection by the detector 50. At step 122, the emptysample receiving cell area 18 (FIG. 1 a) is illuminated with light fromthe light source 12. When no sample is present in the sample receivingarea, the transmission level through the system 10 is very high (e.g.,nearly 100%). At step 124, the sample is input to the sample cellreceiving area 18. According to one embodiment of the present invention,the reagent to be mixed with the sample has already been dried in placedin the sample cell receiving area 18. Alternatively, the reagent may bedeposited with the sample or after the sample has been received in thesample cell receiving area 18.

The system 10 monitors the sample cell receiving area 18 by measuringthe light transmitted through the sample at step 126. The system 10compares the amount of transmitted light measured by the detector 50 toa threshold stored in a memory of the system 10 at step 128. If themeasured amount of light exceeds the threshold, the system determinesthat a requisite amount of sample has not been input to the sample cellreceiving area at step 128, and the amount of light transmitted throughthe sample cell receiving area 18 is re-measured at step 126. The system10 may wait a predetermined amount of time (e.g., 5 or 10 seconds) atstep 130 before taking the next measurement. If the measured amount oflight is less than the threshold stored in memory, the system then maybegin the analysis at step 150 (FIG. 2 b) or step 102 (FIG. 2 c).

While measuring the transmitted light at step 126 has been illustratedas occurring after inputting the sample to the sample receiving area,this step may be performed in a continuous manner. For example, thedetector may continuously detect light transmitted through the samplecell receiving area 18 for purposes of determining when to begin theanalysis set forth in FIG. 2 c from the moment the system 10 hasstarted-up to when a positive determination at step 128 occurs.Additionally, the system 10 may generate an error signal if a positivedetermination has not been made after a sample is input to the samplecell receiving area at step 124 (e.g., too little sample input after thesystem 10 has been started) according to an alternative embodiment.Additionally, it is desirable to know exactly when the reaction beginsoccurring to accurately determine the reaction time of the assay. Theprecise time for the start of the reaction may be determined by usingthe monitoring method of FIG. 2 a.

The total transmission spectroscopy system is adapted to collect asubstantially improved amount of transmitted light in the visible range(e.g., from about 400 to about 700 nm) and in the near-infrared range(e.g., from about 700 to about 1100 nm) over regular transmissionsystems for determining the analyte concentration in a sample. Thetransmission spectroscopy system 10 provides performance advantages overexisting total transmission systems because a high percentage of thecollected transmitted light illuminates the detector. This improvedcollection capability permits the system 10 to collect light in thesetwo regions, which are used in correcting for the bias or interferencecaused by scatter due to different hematocrit levels (FIG. 2 b) or thepresence of both hemoglobin (FIG. 2 c) and hematocrit (FIG. 2 c) in abody fluid such as a whole blood sample.

Referring now to FIG. 2 b, one method of using the transmissionspectroscopy system 10 to determine the analyte concentration in a bodyfluid (e.g., a whole blood sample) and to correct for the transmissionbiases caused by different hematocrit levels is shown. The degree ofbias is a function of the hematocrit level in the whole blood sample.The indicator reagents are designed to produce chromatic reactionsindicative of the blood sample's analyte concentration levels at visiblelight wavelengths less than about 750 nm according to one embodiment ofthe present invention.

In experimenting with the total transmission system 10 of FIG. 1 a, itis believed that the total transmitted light varies with hematocritlevel when measured at visible and near IR wavelengths from about 400 toabout 1100 nm. Prior to the inventors' discovery, it was commonly heldthat separation between hematocrit levels could not be detected withtotal transmitted light having wavelengths ranging from about 600 toabout 1000 nm. For example, the Journal of Biomedical Optics articlediscussed in the Background Section shows no separation betweenhematocrit levels at wavelengths from about 600 to about 800 nm.

The hematocrit level of whole blood, however, does affect the spectralresponse throughout the visible and near IR (“infrared”) light regions(e.g., 400 to 1100 nm). The light transmission varies with and isproportional to different hematocrit levels because of differences inthe scattered light due to the number of red blood cells. The hematocrittransmission bias at near IR wavelengths is proportional to thehematocrit level of the blood. A comparison between FIGS. 3 a and 3 balso shows that the transmission of 20% hematocrit blood is 30% T higherthan a 60% hematocrit blood sample throughout the tested range fromabout 500 to about 940 nm. The transmission measured at near-IRwavelengths, however, is not affected by changes in glucoseconcentration because the indicator is designed to react and produce achromatic response at visible wavelengths (e.g., about 680 nm).

In operation, according to one process shown in FIG. 2 b, a whole bloodsample reacted with reagent is illuminated with a first wavelength oflight (e.g., from about 750 to about 1100 nm) at step 150 fordetermining the scattered portion of the measured light due tohematocrit levels in the whole blood sample. The light—normal andscattered—is measured with the detector 50 at step 152 as is describedabove in connection with FIG. 1 a. Next, the sample is illuminated witha second wavelength of light (e.g., from about 600 to about 750 nm) atstep 154, and the transmitted normal and scattered light is measuredwith the detector 50 at step 156 for determining both the scatted lightdue to hematocrit level and the chromatic response due to analyteconcentration. The bias due to hematocrit-dependent scattered light iscorrected for at step 158 by calculating the ratio of the transmissionmeasurements obtained at steps 156 and 152. The analyte concentrationlevel of the whole blood sample is calculated at step 160 using thecorrected transmission from step 158.

In alternative embodiments of the present invention, additionalcorrection algorithms such as, for example, linear regression orpolynomial-fit correction algorithms may be used to determine therelationship between the hematocrit level and the bias, or interference,caused by the hematocrit at the wavelength where the analyte reactionoccurs.

Turning to FIG. 2 c, a method of using the transmission spectroscopysystem 10 to determine the analyte concentration in, for example, awhole blood sample and to correct for the transmission bias caused bythe presence of hemoglobin is shown. The degree of bias is a function ofthe hemoglobin level in the whole blood sample and the scatter due tothe presence of red blood cells. In operation, the reaction of the wholeblood sample and the reagent is illuminated with light at firstwavelength from about 400 to about 600 nm at step 102. For example, thefirst wavelength may be about 545 nm or about 577 nm. The light—regularand scattered—is measured in absorbance units with the detector 50 atstep 104 as is described above in connection with FIG. 1 a.

As discussed in the Background Section, the spectra of oxy-hemoglobinshows absorbance peaks at about 545 nm and about 577 nm and is notaffected by reaction at these wavelengths, because the reaction isdesigned to be measured at, for example, a second wavelength about 750nm. The absorbance measured at the first wavelength includes thecontribution of both the hemoglobin and the scatter due to hematocritlevel of blood. According to one embodiment, the indicator reagentsproduce a chromatic reaction indicative of the blood sample's analyteconcentration level at a second wavelength greater than about 600 nm andless than about 1000 nm (visible-near infrared). The whole blood sampleand the reagent are illuminated with light at second wavelength at step106.

The bias due to the presence of the hemoglobin in the whole blood sampleis corrected for at step 110 by using the measurement obtained at step104 to correct for the bias affecting the measurement obtained at step108. The method for correcting the bias depends on the correlationbetween the hemoglobin concentration and the bias of measurement 108caused by hemoglobin. The correlation may be linear or non-lineardepending on the chemistry formulation that is used in the reaction. Theanalyte concentration of the sample is determined in step 112 using thecorrected transmission measurement from step 110.

Similar to that discussed above in connection with FIG. 2 b, the methodfor determining the presence of an adequate sample and the start time ofthe reaction illustrated in FIG. 2 a may also be applied to the methodof FIG. 2 c in another process.

As discussed above, the transmission spectroscopy system 10 of thepresent invention is adapted to collect a substantially improved amountof transmitted light in the visible range and in the near-IR range overregular transmission systems for determining the analyte concentrationin a sample. In experimenting with the total transmission system 10 ofFIG. 1 a, it is believed that hematocrit level or hemoglobin may causetransmission bias at the read wavelength where a reagent indicator has achromatic reaction. A transmission bias that is proportional to thehematocrit level occurring at first read wavelength (e.g., greater than750 nm) may be used to correct a second read wavelength (e.g., fromabout 600 to 750 nm) that includes both the bias due to the hematocritlevel and the chromatic reaction of the chemical indicator.Alternatively, a transmission bias that is proportional to hemoglobinoccurring at a first read wavelength (e.g., less than 600 nm) may beused to correct a second read wavelength (e.g., greater than 600 nm)where the chemical indicator causes a chromatic reaction.

EXAMPLES

Referring now to FIG. 3 a, one embodiment of the present invention(transmission spectroscopy system 10) measured the total transmissionlevels of whole blood samples having hematocrit levels of 20% reactedwith reagents, and each had a different glucose concentration level—54,104, 210, and 422 milligrams of glucose per deciliter of blood (“mg/dLglucose”). The transmission spectroscopy system 10 will be referred toin the examples as the “inventive system.” White light from the lightsource 12 (FIG. 1 a) was transmitted through the sample. The totaltransmission level measured from 500 nm to 940 nm was plotted in FIG. 3a for each of the glucose concentration levels. The transmission waslower from 500 to 600 nm due to the absorption of hemoglobin.Transmission loss caused by light scattered by red blood cells(hematocrit) affects the transmission from 500 nm to 940 nm. Theindicator in the glucose reaction absorbs between 500 and 750 nm, sothere was separation between the glucose concentration levels up toabout 750 nm. As shown in FIG. 3 a, at wavelengths above about 750 nm,the decrease in the total transmission level was due only to light lossfrom the scatter by red blood cells, so there was little separationbetween the samples having different glucose concentration levels.

FIG. 3 b shows that the total transmission level decreases throughoutthe measured wavelength range from 500 nm to 940 nm when the hematocritlevel of blood is increased to 60% for blood samples having similarglucose concentrations as those plotted in FIG. 3 a (59, 117, 239, and475 mg/dL glucose). FIG. 3 b also shows separation between the glucoseconcentration levels from 500 to about 750 nm. As shown in FIG. 3 a, thetransmission level about 750 nm was between 70 to 80% for the bloodhaving a hematocrit level of about 20%. As shown in FIG. 3 b, thetransmission level above 750 nm was between 40 to 50% for the bloodhaving a hematocrit level of about 60%. The differences between thespectra at 20% and 60% hematocrit were proportional for wavelengths fromabout 600 nm to 940 nm, above the wavelengths where there isinterference due to the absorption by hemoglobin.

There, however, was little separation between the glucose concentrationlevels at wavelengths above 750 nm for either level of hematocrit inFIG. 3 a or 3 b. Thus, the 750 to 940 nm spectrum may be used todetermine the level of hematocrit caused by differences in the number ofred blood cells in these levels. The hematocrit level is not dependenton glucose concentration or hemoglobin at those wavelengths. The lighttransmission due to scattered light (determined using near-IRwavelengths) is used to correct for the interference due to hematocritlevel before determining the glucose concentration level.

FIGS. 4 a, 4 b show plots of the total transmission spectra ofrespective FIGS. 3 a, 3 b corrected for scatter by ratioing alltransmission readings to the transmission at 940 nm. After correction,similar transmissions for similar glucose concentrations are obtainedfor both the 20% and 60% hematocrit blood samples in the wavelengthrange where the indicator reaction for the glucose assay is measured(about 660 nm to 680 nm). Thus, the near-IR wavelengths may be used tocorrect for differences due to hematocrit of the whole blood sample. Theability to correct for this interference error improves the accuracy ofglucose concentration measurements.

Referring now to FIG. 5, the manner in which the hematocrit level isused to correct the glucose concentration measurement is discussedaccording to one embodiment. The total transmission response is shownfor whole blood at hematocrit levels (“Hct”) of 20%, 40%, and 60% inFIG. 5, wherein the transmission (in absorbance units) for visible lighthaving a wavelength of about 680 nm is plotted against glucoseconcentration level. Similar dose responses are observed at eachhematocrit level, but there is a bias or interference caused by therespective hematocrit levels as shown by the separation between thethree hematocrit levels plotted in FIG. 5.

FIG. 6 shows the same data where the bias due to different hematocritlevels is corrected by a ratio of the visible light at about 680 nmdivided by the near-IR light from about 750 to about 940 nm that istransmitted through a blood sample. The correction is accomplished bydividing the transmission level of the visible light at 680 nm (FIG. 5)by the transmission level of near-IR light at 940 nm for the sample asdiscussed above. Put simply, the hematocrit bias due to differences inscatter is “subtracted out”, and FIG. 6 shows a dose response that isnot affected by changes in hematocrit level.

Referring now to FIG. 7, the inventive system was used to measure theglucose concentration of several samples of whole blood. Dried reagentswere reconstituted with blood samples having a glucose concentration of0, 100, and 400 mg/dL. Additionally, a 0 mg/dL blood sample with noreagent, and dried reagents reconstituted with a water sample. The bloodsample without chemistry shows the spectral contribution of blood, whilethe water sample with reagent shows the spectral contribution of thereagent. The total absorbance levels of the reactions were recorded on aspectrograph every 5 seconds to a total test time of 60 seconds. Thereaction was completed in 15 to 30 seconds. This is considerably fasterthan regular transmission spectroscopy, which depends on a extendedreaction time of from about 60 to 90 seconds required to complete redblood cell lysis. As shown in FIG. 7, there was separation in thetransmission levels of light between the various glucose concentrationlevels—0, 100, and 400 mg/dL—at visible wavelengths (e.g., from about660 to about 680 nm), which are used to determine the glucoseconcentration levels.

Referring now to FIG. 8, the inventive system was used to measure the680 nm light transmitted through several whole blood samples havingknown glucose concentrations. In FIG. 8, the total transmitted light(plotted in absorbance units) levels were plotted against the knownglucose concentration levels of the whole blood. A linear regressionanalysis was applied to the data plotted in FIG. 8. As shown, there is asubstantially linear relationship between the amount of transmittedlight and the glucose concentration. The linear correlation coefficientof 0.985 (nearly 1.000)—demonstrates that there was excellentcorrelation between the absorbance level and the glucose concentrationusing the system and method of the present invention.

Referring to FIG. 9, the total transmission levels for three whole bloodsamples having hematocrit levels of 20%, 40%, and 60%, respectively,were obtained using the inventive system. Light having wavelengths fromabout 500 to about 940 nm was transmitted through the whole bloodsamples. The pathlength of the sample receiving cell was 42 micrometers.In FIG. 9, the transmission levels for the three samples obtained wereplotted against the wavelength of the transmitted light.

To illustrate the advantages of one embodiment of the inventive systemover an existing spectroscopy system using a regular transmission system(“regular system”), the transmission levels for three whole bloodsamples having hematocrit concentration levels of 20%, 40%, and 60% areshown for both methods in FIG. 9. The regular transmission system islabeled in FIG. 9 as “% Hct, regular % T”, and the total transmissionsystem is labeled in FIG. 9 as “% Hct, Total % T”. Both transmissionsystems used in this example illuminated the three samples withsubstantially collimated light having the wavelengths from about 500 toabout 940 nm. The substantially collimated light, and not the scatteredlight, transmitted through the samples, was collected with the regulartransmission system, while both regular and scattered light is collectedby the inventive system. In both transmissions systems, the sample pathlength was about 42 μm.

Comparing the two sets of data in FIG. 9, the regular transmission levelof light for the three samples is less than 2% at wavelengths greaterthan 500 nm. The transmission levels of light collected for the threesamples obtained with the inventive system were greater than 10% T atwavelengths greater than 500 nm. Good separation between thetransmission levels for the three samples obtained with the inventivesystem occurred for light having wavelengths of greater than 500 nm.FIG. 9 also shows that, for the data obtained with the inventive system,dips occurred in the transmission levels at from about 542 to about 577nm. These two wavelengths of light correspond to the known absorbancepeaks of oxy-hemoglobin. Thus, as shown in FIG. 9, the describedembodiment of the inventive system achieved a greater amount oftransmitted light from 500 to 940 nm over the existing spectroscopysystem using a regular transmission system, despite the absorbance ofhemoglobin or the light scattered by hematocrit at these wavelengths.

In another embodiment, bias caused by scatter due to imperfections inthe sample cell or small amounts of debris in the sample can becorrected in a manner similar to that for different hematocrit levels,as discussed in conjunction with in FIG. 2 b. The two read wavelengthsratio corrects for contamination on the sample cell such asfingerprints, or sample cell mold defects, or scratches in the windows.This correction significantly improves assay precision compared to usingone wavelength.

In another embodiment, the wavelength range where a change in absorbanceverses glucose concentration occurs outside the wavelength range wherehemoglobin absorbs light (e.g., wavelengths greater than about 600 nm).Use of an indicator reagent that develops at wavelengths greater thanabout 600 nm may also be used so that the hemoglobin absorbance peaksand the indicator reagent would not interfere with each other. FIG. 9also shows that, for the data obtained with the inventive system, dipsoccurred in the transmission levels at about 530 nm and about 570 nm.These two wavelengths of light correspond to the known absorbance peaksof oxy-hemoglobin. The absorbance reading at about 542 nm or 577 nm maybe used to determine the concentration of hemoglobin after subtractingout the contribution due to scatter from the red blood cells as measuredin the near-IR (from about 750 to 1100 nm). In this case, the absorbanceof visible light having a wavelength of about 542 nm would not change orbe dependent on glucose concentration.

As discussed in the Background Section, decreasing the pathlength couldincrease the transmission level of the regular transmission method. Themechanical tolerances that affect the pathlength are well known to thoseof skilled in the art to cause a proportional error in glucoseconcentration. Therefore, the longer pathlength provided by the totaltransmission spectroscopy system of the present invention results inless glucose concentration error.

Alternate Embodiment A

A total transmission spectroscopy system for use in determining theconcentration of an analyte in a fluid sample, the system comprising:

a sample cell receiving area for receiving a sample to be analyzed, thesample cell receiving area being constructed of a substantiallyoptically clear material;

a light source;

a collimating lens being adapted to receive light from the light sourceand adapted to illuminate the sample cell receiving area with asubstantially collimated beam of light;

a first lens being adapted to receive regular and scattered lighttransmitted through the sample at a first angle of divergence, the firstlens receiving light having a first angle of acceptance, the first lensoutputting light having a second angle of divergence, the second angleof divergence being less than the first angle of divergence;

a second lens being adapted to receive light from the first lens andadapted to output a substantially collimated beam of light; and

a detector being adapted to measure the light output by the second lens.

Alternate Embodiment B

The system of Alternate Embodiment A wherein the fluid sample is bloodand wherein the sample cell receiving area includes a dried reagent inthe absence of a hemolyzing agent is adapted to produce a chromaticreaction when reconstituted with blood.

Alternate Embodiment C

The system of Alternate Embodiment A wherein each of the first andsecond lenses is a half-ball lens.

Alternate Embodiment D

The system of Alternate Embodiment A wherein the first lens has a firstangle of acceptance of from 0 to about 90 degrees.

Alternate Embodiment E

The system of Alternate Embodiment A wherein the first lens has a firstangle of acceptance angle greater than 70 degrees.

Alternate Embodiment F

The system of Alternate Embodiment A wherein the second angle ofdivergence of the first lens is from about 15 to about 40 degrees.

Alternate Embodiment G

The system of Alternate Embodiment A wherein the ratio of the diametersof the first lens to the second lens is from about 1:2.

Alternate Embodiment H

The system of Alternate Embodiment A wherein the light source outputslight having a wavelength of from about 500 to about 940 nm.

Alternate Embodiment I

The system of Alternate Embodiment A wherein the light source comprisesa light-emitting diode.

Alternate Embodiment J

The system of Alternate Embodiment A wherein the light source outputsmonochromatic light.

Alternate Embodiment K

The system of Alternate Embodiment A wherein the light source outputswhite light.

Alternate Embodiment L

The system of Alternate Embodiment A wherein the detector comprises asilicon detector.

Alternate Embodiment M

The system of Alternate Embodiment A wherein the fluid is blood.

Alternate Embodiment N

The system of Alternate Embodiment A wherein the analyte is glucose.

Alternate Embodiment O

The system of Alternate Embodiment A wherein the first lens receivessubstantially all of the regular and scattered light transmitted throughthe sample.

Alternate Embodiment P

The system of Alternate Embodiment A further comprising a filter adaptedto select a specific wavelength from the light source.

Alternate Embodiment Q

The system of Alternate Embodiment A further comprising a coupling lensand fiber optic cable for piping light from the second lens to thedetector.

Alternate Embodiment R

The system of Alternate Embodiment A wherein the substantiallycollimated beam of light output by the second lens has an angle ofdivergence of less than about five degrees.

Alternate Process S

A method for use in determining the analyte concentration in a fluidsample with a total transmission spectroscopy system, the methodcomprising the acts of:

receiving a sample to be analyzed in a sample cell receiving area of thetotal transmission spectroscopy system;

outputting a beam of light via a light source;

substantially collimating the beam of light output from the lightsource;

illuminating the sample with the substantially collimated beam of lightoutput from the light source;

collecting regular and scattered light transmitted through the samplewith a first lens;

reducing the angle of divergence of the transmitted light with the firstlens;

receiving the light having a reduced angle of divergence with a secondlens;

substantially collimating the received light with the second lens; and

measuring the substantially collimated light from the second lens with adetector.

Alternate Process T

The method of Alternate Process S wherein each of the first and secondlenses is a half-ball lens.

Alternate Process U

The method of Alternate Process S wherein the reduced angle ofdivergence with the first lens is from about 15 to about 40 degrees.

Alternate Process V

The method of Alternate Process S wherein the received light with thesecond lens reduces the angle of divergence of the light diverging fromthe second lens to less than about 5 degrees.

Alternate Process W

The method of Alternate Process S wherein the light source has awavelength from about 500 to about 940 nm.

Alternate Process X

The method of Alternate Process S wherein the light source outputs amonochromatic beam of light.

Alternate Process Y

The method of Alternate Process S wherein the light source is whitelight.

Alternate Process Z

The method of Alternate Process S further comprising monitoring thedetector for determining when the sample cell receiving area hasreceived a predetermined amount of sample to be analyzed.

Alternate Process AA

The method of Alternate Process Z further comprising determining theanalyte concentration in the fluid sample after determining the samplecell receiving area has received a predetermined amount of sample to beanalyzed.

Alternate Process BB

A method for measuring light transmitted through a fluid sample with atotal transmission spectroscopy system, the method comprising the actsof:

illuminating the sample with a substantially collimated beam of light;

collecting regular and scattered light transmitted through the samplewith a first lens;

reducing the angle of divergence of the transmitted light with the firstlens;

substantially collimating the transmitted light with a second lens afterreducing the angle of divergence; and

measuring the substantially collimated transmitted light with adetector.

Alternate Process CC

The method of Alternate Process BB wherein each of the first and secondlenses is a half-ball lens.

Alternate Process DD

The method of Alternate Process BB wherein reduced angle of divergencewith the first lens is from about 15 to about 40 degrees.

Alternate Process EE

The method of Alternate Process BB wherein substantially collimating thereceived light with the second lens comprises reducing the angle ofdivergence of the light received with the second lens to less than about5 degrees.

Alternate Process FF

The method of Alternate Process BB further providing a light sourceadapted to output a beam of light further with a wavelength of fromabout 500 to about 940 nm.

Alternate Process GG

The method of Alternate Process BB further providing a light sourceadapted to output a beam of light with a monochromatic beam of light.

Alternate Process HH

The method of Alternate Process BB further providing a light sourceadapted to output a beam of light of white light.

Alternate Process II

The method of Alternate Process BB wherein collecting normal andscattered light comprises collecting substantially all of the normal andscattered light transmitted through the sample.

Alternate Process JJ

The method of Alternate Process BB further comprising monitoring thedetector adapted to determine when the sample cell receiving area hasreceived a predetermined amount of sample to be analyzed.

Alternate Process KK

The method of Alternate Process JJ further comprising determining theanalyte concentration in the fluid sample after determining the samplecell receiving area has received a predetermined amount of sample to beanalyzed.

Alternate Process LL

A method for determining the concentration of an analyte in a fluidsample using a total transmission spectroscopy system, the systemincluding a first lens adapted to receive regular and scattered lighttransmitted through the sample, a second lens adapted to receive lightfrom the first lens and adapted to output a substantially collimatedbeam of light, a light source and a sample cell receiving area, themethod comprising the acts of:

reacting the sample with a reagent adapted to produce a chromaticreaction in a sample cell receiving area of the system;

illuminating the sample with a substantially collimated beam ofnear-infrared light output by the light source of the system;

measuring the near-infrared light transmitted through the sample with adetector of the system;

illuminating the sample with a substantially collimated beam of visiblelight output by the light source of the system;

measuring the visible light transmitted through the sample with thedetector; and

determining a ratio of the measured visible light to the measurednear-infrared light transmitted through the sample.

Alternate Process MM

The method of Alternate Process LL wherein the fluid sample is blood.

Alternate Process NN

The method of Alternate Process LL wherein the analyte is glucose.

Alternate Process OO

The method of Alternate Process LL wherein determining the ratioincludes factoring out the transmission bias caused by the hematocritlevel in the blood sample.

Alternate Process PP

The method of Alternate Process LL wherein the enzyme is glucosedehydrogenase coupled with a mediator that produces color with atetrazolium indicator.

Alternate Process QQ

A method for determining the glucose concentration in a blood sampleusing a total transmission spectroscopy system, the system including afirst lens adapted to receive regular and scattered light transmittedthrough the sample and a second lens adapted to receive light from thefirst lens and adapted to output a substantially collimated beam oflight, the method comprising the acts of:

reacting the blood sample with a dried reagent to produce a chromaticreaction in a sample cell receiving area;

illuminating the sample with a substantially collimated beam of visiblelight output by a light source of the system;

measuring the visible light transmitted through the sample with adetector of the system;

illuminating the sample with a substantially collimated beam ofnear-infrared light output by the light source;

measuring the near-infrared light transmitted through the sample withthe detector;

correcting for transmission bias caused by hematocrit level of the bloodsample; and

determining the glucose concentration in the blood sample.

Alternate Process RR

The method of Alternate Process QQ wherein correcting comprisesdetermining a ratio of the measured visible light and the measurednear-infrared light transmitted through the sample.

Alternate Process SS

The method of Alternate Process QQ wherein correcting comprisesdetermining a correlation between the measured visible light and themeasured the near-infrared light transmitted through the sample andapplying the correlation correction to the visible light transmissionmeasurement.

While the invention is susceptible to various modifications andalternative forms, specific embodiments are shown by way of example inthe drawings and described in detail. It should be understood, however,that it is not intended to limit the invention to the particular formsdisclosed, but on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

1. A method of determining glucose concentration of a whole blood sampleusing an optical test sensor, the method comprising: providing anoptical test sensor including a reagent composition having an enzyme;measuring transmission levels at two different wavelengths of the wholeblood sample; correcting absorbance bias of the whole blood sample, ifany, caused by hematocrit levels using the transmission levels at twodifferent wavelengths; and determining the glucose concentration usingthe measured transmission levels and corrected absorbance bias, if any,of the whole blood sample.
 2. The method of claim 1 wherein the twodifferent wavelengths includes a visible light wavelength and a near-IRlight wavelength.
 3. The method of claim 2 wherein the near-IR lightwavelength is from about 700 to about 1,100 nm.
 4. The method of claim 2wherein the near-IR light wavelength is from about 750 to about 940 nm.5. The method of claim 2 wherein the visible wavelength is from about400 to about 700 nm.
 6. The method of claim 2 wherein the visiblewavelength is from about 660 to about 680 nm.
 7. The method of claim 1wherein the correction is a ratio of a measured transmission level of avisible light and a measured transmission level of a near-IR lightwavelength.
 8. The method of claim 7 wherein the visible wavelength isfrom 400 to 700 nm and the near-IR light wavelength is from 700 to 1,100nm.
 9. The method of claim 7 wherein the visible wavelength is fromabout 660 to about 680 nm and the near-IR light wavelength is from 700to 1,100 nm.
 10. The method of claim 7 wherein the visible wavelength isfrom about 660 to about 680 nm and the near-IR light wavelength is from700 to 940 nm.
 11. The method of claim 1 wherein bias due to hematocritis within +/−10%.
 12. The method of claim 1 wherein bias due tohematocrit is within +/−10% between 20% to 60% hematocrit levels. 13.The method of claim 1 wherein bias due to hematocrit is within +/−5%.14. The method of claim 1 wherein bias due to hematocrit is within+/−10% between 20% to 60% hematocrit levels.
 15. A method of determiningglucose concentration of a whole blood sample using an optical testsensor, the method comprising: providing the optical test sensorincluding a reagent composition having an enzyme; contacting the wholeblood sample with the reagent composition; measuring the glucoseconcentration of the whole blood sample; correcting bias of the wholeblood sample, if any, caused by a hematocrit level; and determining theglucose concentration using the measured glucose concentration and thecorrected bias, if any, of the whole blood sample wherein the bias dueto the hematocrit level of the determined glucose concentration iswithin +/−5% between 20% to 60% hematocrit levels.
 16. The method ofclaim 15 wherein the determined glucose concentration is between 100 and400 mg/dL.